Air heater



Dec. 24, 1957 E. c. MILLER 2,817,498

AIR HEATER Filed Oct. 30. 1952 INVENTOR EARL; C. MILLER ATTORNEY nitedStates Patent AIR HEATER Earle C. Miller, Worcester, Mass, assignor toRiley Stoker Clprporation, Worcester, Mass., a corporation of Massacusetts Application October 30, 1952, Serial No. 317,744

2 Claims. (Cl. 257224) This invention relates generally to air heatersand more particularly to a heater apparatus for supplying air at aplurality of temperatures.

t is common practice in the steam generating art to make use ofcombustion gases to heat the incoming air that is to be used forcombustion and like purposes. Usually combustion gases are used whichhave already passed through the boiler and which are at a relatively lowtemperature. in most furnaces associated with steam generatingequipment, it is necessary and desirable to have air available at anumber of different temperatures. For example, in the operation of aspreader stoker with a traveling grate, air at one temperature is neededfor introduction under the grate and for passage upwardly therethroughand air at another temperature is needed for overfire jets to promotecomplete combustion and to prevent smoking. Apparatus for providing formultitemperature air have in the past been complicated and expensiveand, furthermore, have not permitted a wide range in differences in airtemperature. The present invention obviates these disadvantages in anovel manner.

It is therefore an outstanding object of the present invention toprovide an air heater apparatus which will provide air at differenttemperatures for use in a furnace.

It is another object of the invention to provide a novel heat-exchangemeans for providing for heating of air to a plurality of widelydivergent temperatures.

Another object of this invention is the provision of an air heater ofsimple and inexpensive construction.

Still another object of the instant invention is the provision of an airheater particularly adapted to providing heated air for a furnace havinga spreader stoker with a traveling grate, the air to be used under thegrate and in overfire jets.

The various features of novelty which characterize my invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawings and descriptivematter in which I have illustrated and described a preferred embodimentof my invention.

The single sectional view shows a preferred embodiment of the invention.

Referring to the drawing, an air heater 10, constructed according to theprinciples of the invention, is shown in use with a steam generatingunit 11, having a furnace 12 and a boiler 13. The furnace 12 has aforward wall 14, a rear wall 15, side Walls 16, and a top wall 17defining a combustion chamber 1%. At the lower portion of the furnace 12and forming a bottom for the combustion chamber is a traveling grate 19of the usual type having a plenum chamber 24 on its under side andprovided with partitions 21 to permit control of air flow to variouscertain sections of the grate. Mounted on the outer side of the forwardwall 14 is a spreader stoker 22 of the type having a rotary distributor23; an opening 24 in the 2,817,498 Patented Dec. 24, 1957 forward wallis provided to permit fuel to be thrown into the furnace and onto thegrate 19 by the stoker. The rear wall 15 is formed to provide an arch 25overlying one end of the grate and at the nose of the arch is provided ahorizontal row of overfire air nozzles 26. Another such row of nozzles27 is provided at a higher position in the rear wall.

The boiler 13 is situated at the upper rear of the furnace and consistsof an upper steam-and-water drum 28 and a lower mud drum 29 joined bydowncomer tubes 30 and steaming tube 31. A refractory wall 32 extendsupwardly from the mud drum 29 and constitutes an extension of the rearWall 15 of the furnace. The upper edge of the Wall 32, the rear portionof the top wall 17, and the side walls 18 define a gas pass 33 at theupper, rear portion of the furnace. A baffle 34 hangs from thesteam-and-Water drum 28 between the downcomer tubes 30 and the steamingtubes 31 and extends to within a substantial distance of the mud drum29. Directly behind the downcomer tubes 3% is a back wall 35 whichculminates at its lower portion in a fly-ash hopper 36. The back wall 35and the battle 34 define a back gas pass 37 which merges with a largehorizontal gas duct 38. The duct 38 is connected with the breeching 39leading to the stack, not shown, by a bundle 40 of vertical gas tubeswhich are part of the air heater 10. Parallel to the bundle 4t andspaced rearwardly therefrom is a wall 41, the top portion of which isconnected to the lower wall 45 of the duct 38 and the lower portion ofwhich is attached to the top wall of an air entrance duct 42 which isserved by a fan 4-3. A forward wall 44 resides forwardly of the bundle4d and is spaced therefrom. The outer envelope of the air heater 10 isgenerally defined, therefore, by the forward wall 44, the rear wall 41,the lower wall 45 of the duct 38, the lower wall 46 of the duct 42, andside walls 47, only one of which is seen in the drawing. The upper wall48 of the duct 42 extends horizontally toward the forward wall 44 andends at a position somewhat spaced therefrom. A first baffle 49 extendshorizontally from the wall 44 toward the rear wall 41 and ends at aposition substantially spaced from the said rear wall; this baffleresides above and spaced from the upper wall 48 of the duct 42. A secondbaffle 50 extends from the rear wall 41 toward the forward wall 44 andends at a position substantially spaced therefrom; this baffle is aboveand spaced from the baffle 49. A third baffle 51 extends rearwardly fromthe top edge of the forward wall 44, which edge is spaced substantiallyfrom the lower wall 45 of the duct 38. The baffle 51 extendshorizontally to within a substantial distance of the rear wall 41.

Midway between the bafiles 49 and 51 and aligned with the baffle 50 isan opening 52 in the forward wall and this opening is provided with amovable shutter or damper 53 which is adjustable from the outside of theapparatus. The damper pivots on a horizontal axis which is medial of theopening 52. A similar opening 54 and damper 55 is provided midwaybetween the baflie 49 and the lower wall 46 of the duct 42, the openingbeing centered somewhat above the plane of the upper wall 48 of the duct42. A wall 56 is situated parallel to and substantially spaced from theforward wall 44, the wall 56 serving, with the forward Wall 44 and theside walls 47, to define an outer mixing chamber 57. The upper portionof the wall 56 and the upper edge of the forward wall 44 define anopening 58 into the mixing chamber 57 and a damper 59 resides therein.The bottom of the mixing chamber 57, defined by the lower edges of thewalls 44 and 56, is connected to one end of a hot air duct 60, the otherend of which is connected to the plenum chamber 20 of the travelinggrate 19. The upper end of the air heater 1!) has an 24 in the forwardWall of the furnace by the rotating distributor 23. The coal passesthrough the air in a pattern determined by the characteristics of theStoker and the fines are burned in suspension, while the heavierportions of the fuel fall onto the traveling grate 19 where they burnunder the influence of air passing upwardly through the grate from theplenum chamber 20. The hot products of combustion pass upwardly throughthe combustion chamber 18, heating water in the water wall tubes and incertain portions of the steaming tubes by radiation. The gases passupwardly and pass rearwardly through the pass 33. From there they passdownwardly between the wall 32. and the baffle 34 heating the steamingtubes 31 by convection. The gases are reversed at the lower end of thebaiile 34 and proceed upwardly in the back pass 37, but not beforedepositing a certain amount of fly-ash and cinder in the hopper 36.After passing upwardly through the back pass 37 and heating the water inthe downcomer tubes 30 by convection, the gases enter the duct 38 andpass horizontally therealong. From the duct 33 the gases enter the upperends of the tubes comprising the bundle 40, pass downwardlytherethrough, and leave at the lower ends into the breeching 39, fromwhence they eventually pass into the stack. While the gases reside inthe tube bundle 48 they are in heat exchange relation to any air whichmay reside extcrnally of the tube bundle. Air enters the air heaterthrough the inlet duct 42 under the influence of the fan 4-3. if thedampers '5, 53, and 59 are closed, the air will leave the duct 42, afterhaving passed through the portion of the tube bundle which resides inthe duct, and makes a. reverse turn around the forward edge of the upperwall lb of the duct. Air then passes horizonta ly between the upper wall48 and the baffle 49 and then makes an upwardly reverse turn around thefree rearward edge of the baffie 49. It then passes horizontally betweenthe baffle 49 and the baffle 50 before making a reverse turn around thefree forward edge of the baflle fill. The air then passes horizontallybetween the baffles 5 and 51 and then makes a reverse turn around thefree rearward edge of the baffie 51 and enters the horizontal passagebetween the bathe 51 and the lower wall 45 of the duct It then leavesthe air heater through the opening 6i and flows through the duct 62 tothe chambers 63 and 64- for distribution to the nozzles 27 and 26. Airthus delivered to the nozzles 26 and 27 is projected outwardly into thefurnace to promote turbulence and more complete combustion, in thewellknown manner. Now, if any of the dampers 53, 55, and 59 are open,some of the air will be tapped off into the mixing chamber 57, fromwhence it will flow into the duct Hill and through that duct into theplenum charm ber 2t). Air delivered to the plenum chamber is distributedby the partitions 21 to various portions of the grate and flows upwardlythrough the grate in the wellknown manner to support combustion.

it can be seen, then, that adjustment of the dampers 53, 55, and 59 willbring about any desirable air temperature for delivery to the overfirejets and the grate. Any air which flows through the air heater it)without being tapped off into the mixing chamber 57 must necessarilypass outwardly into the conduit 62; such air has passed over all thetube surface in the bundle at and has not only been in contact with theheated surface of the tubes for the greatest length of time possible,but has also been in heat exchange relation to the hottest gases as theypass through the tubes at the upper portion of the bundle. If it isdesired to have very hot air enter the chamber 57 for use under thegrate, it is only necessary to close all the dampers but damper 5'9,whereupon the air entering the chamber will be at the same temperatureas the air entering the duct 62 for use in the overfire jets. With suchoperation, the two air streams will be at the same high temperature. Ifrelatively cold air is desired under the grate, it is only necessary toclose all the dampers except damper 55, in which case the air tapped offrate the chamber 57 will have passed only over the small part of thetube bundle which resides in the duct 42. During this manner ofoperation of the apparatus, the temperature difference between the jetair and tin grate air is very great. In this connection it is to benoted that when air is tapped off early in the cycle of heating, thereis a smaller flow of air through the remainder of the air heater, sothat the air velocities are less and the transfer of heat is greater;the air going to the jet will thus be considerably hotter than when allthe air passes through all the heater. It is possible, by judicious useof the dampers, to regulate the manner in which the flow of airoriginating in the fan 43 is di vided between the jets and the grate;furthermore, it is possible to regulate the temperatures of the gaseswhich pass to these portions of the furnace.

While in accordance with the provisions of the statutes 1 haveillustrated and described herein the best form of my invention now knownto me, those skilled in the art will understand that changes may be madein the form of the apparatus disclosed without departing from the spiritof the invention covered by my claims, and that certain features of myinvention may sometimes be used to advantage without a corresponding useof other features.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. Air heater apparatus for use with a steam generating unit, comprisinga casing having a front wall, a rear wall, side walls, and end walls, abundle of parallel tubes extending from one end wall to the other andarranged for the passage therethrough of hot products of combustion, aninlet duct for supplying unheated air to one e1:- treme end of theheater, a first outle duct opening into the said front wall adjacent thesaid one end wall for supplying heated air to one portion of the saidunit, a damper controlling the flow of gas through the front wall intothe first outlet duct, a second outlet duct opening into the said casingadjacent the other said end wall for supply ing heated air to anotherportion of the unit after the air has passed over the entire surface ofthe tubes in the bundle, spaced battles extending partially across thecasing alternately from the front and rear walls transversely of thebundle for causing the air to flow back and forth across the bundle onits way from the inlet duct to the outlet ducts, a bypass duct leadingfrom the first outlet duct to the second outlet duct, a dampercontrolling the flow of gas between the second outlet duct and thebypass duct, the said front wall constituting one wall of the byp ssduct, an opening in the said front wall into the bypass ductintermediate of the end walls, and a damper controlling the flow of airthrough the said opening.

2. Air heater apparatus for use with a steam generating unit having atraveling grate, a back wall, a rear wall, and overfire air nozzlesextending through said rear wall, comprising a vertically-elongatedcasing having a front wall adapted to be located adjacent the rear wallof the unit, a rear wall, side walls and end walls, a bundle of paralleltubes extending vertically from the upper end wall to the lower end walland arranged for the passage downwardly therethrough of hot products ofcombustion, an inlet duct for supplying unheated air through the lowerend of the heater, a first outlet duct opening into the said front walladjacent the said lower end wall for supplying heated air to thetraveling grate for passage upwardly therethrough, a damper controllingthe flow of gas through the front wall into the first outlet duct, asecond outlet duct opening into said casing adjacent the other said endwall for supplying heated air to the overfire air nozzles after the airhas passed over the entire surface of the tubes of the bundle, spacedbaflies extending partially across the casing alternately from the frontand the rear walls transversely of the bundle for causing the air toflow back and forth across the bundle on its way upwardly from the inletduct to the outlet ducts, a by-pass d-uct leading upwardly from thefirst outlet duct to the second outlet duct between the front wall ofthe heater and said back wall of the unit, a damper controlling 6 theflow of gas between the second outlet duct and the by-pass duct, thesaid front wall constituting one wall of the by-pass duct, an opening inthe said front wall into the by-pass duct intermediate of the end walls,and a damper controlling the flow of air through the said opening.

References Cited in the file of this patent UNITED STATES PATENTS1,812,458 Turkus June 30, 1931 2,511,647 Marshall June 13, 19502,578,783 Cruise Dec. 18, 1951

